1. Field of the Invention
The present invention relates to a thin film magnetic head for recording and reproducing information on a perpendicularly movable magnetic medium, and more particularly, to a thin film magnetic head which has particular features of a high recording density and a high resolution while minimizing edge noise, and which can be easily fabricated.
2. Description of the Prior Art
Magnetic heads for perpendicular recording fall roughly into two groups, one called an auxiliary pole excitation type and the other called a main pole excitation type. The former type has a disadvantage which requires disposing an auxiliary pole having an excitation coil on the back side of a recording medium. Therefore, the inductance of the excitation coil must be high and a large distance is required between the main pole and auxiliary pole which reduces recording and reproducing efficiencies.
On the other hand, in the magnetic head of the latter type, both a main magnetic pole and excitation coil are disposed on the same front side of the recording medium. Therefore, the magnetizing efficiency to the recording medium becomes unrelated to the thickness thereof. Various design configurations are proposed with regard to a thin film magnetic head of the main pole excitation type for perpendicular recording and reproducing. An example of this type is disclosed in the following Japanese Unexamined Patent Publication "SHO-55-4730" laid-opened on Jan. 14, 1980, by S. Kawakami et al., A simplified cross section thereof is schematically shown in FIG. 1.
A substrate 52 of soft magnetic material has a cut away portion which is filled subsequently with non-magnetic insulating material 55. The substrate 52 with the filled material 55 forms a slider of the magnetic head. A thin film spiral coil 53 is formed on a side surface of the substrate 52 insulated therefrom by an insulating layer 54, and a main magnetic pole 51 of soft magnetic material is formed on a front portion thereof. A protective layer 56 covers the entire surface. The first example shows that the main magnetic pole 51 forms a single magnetic enclosure or path with the substrate 52 and a recording medium 2, interlinking the spiral coil 53.
Responding to requirements to improve the recording density in the recording medium and enhancing the resolution in reproducing information therefrom, another improved type of a perpendicular magnetic head of the prior art, is disclosed in U.S. Pat. No. 4,546,398 by J. Toda et al, issued Oct. 8, 1985.
FIGS. 2(a) and 2(b) show a plan view and a cross section of one of the embodiments disclosed therein, in which the cross section is taken along the line A-A in FIG. 2(a). A magnetic head 1 comprises a non-magnetic substrate 11 and a main, thin film, magnetic pole 12 formed thereon. An insulating layer 13 is further formed thereon in which a thin film excitation coil 14 having a spiral configuration is buried. An auxiliary magnetic pole 15 is formed on the insulating layer 13 and a protection layer 16 covers the entire surface.
A recording medium 2 has a laminated structure comprising a base layer 21, an underlying layer 22, and a recording layer 23. The underlying layer 22 is a soft magnetic material having a high permeability, and the recording layer 23 is a magnetic material having a high coercive force.
The main magnetic pole 12 has a narrow tip portion 121 in order to concentrate the magnetic flux onto a small area on the recording medium 2. The auxiliary magnetic pole 15 has a protruding portion 151 which contacts the rear end of the main magnetic pole 12. The excitation coil 14 surrounds the protruding portion 15 and both ends of the coil 14 include leads 18 which are connected to an external circuitry for signal processing.
When the coil 14 is excited for recording, a substantial part of the generated magnetic flux flows through a magnetic path interlinking the front (lower half) portion of the excitation coil 14. The magnetic path or enclosure comprises the main magnetic pole 12, the recording layer 23, the underlying layer 22, the recording layer 23 again, and the front portion of the auxiliary magnetic pole 15. The magnetic flux crosses the gap G.sub.0 concentrated by the narrow width of the tip portion 121 of the main magnetic pole, and the strong magnetic field magnetizes the recording layer 23 in perpendicular direction. Next the magnetic flux extends through the underlying layer 22 of soft magnetic material in a lateral direction and returns to the auxiliary magnetic pole 15 crossing the recording layer 23 again. On the return path, the magnetic flux does not strongly affect the recording layer 23, which causes a pseudo-pulse signal during read operation, because the tip portion 152 of the auxiliary magnetic pole facing the recording medium has a broad width and is recessed by a predetermined dimension Dy from the level or plane of the tip portion 121 of the main magnetic pole.
When reproducing information, recorded in the recording medium, the recording medium 2 moves close to the main magnetic pole, and a transition of the perpendicular magnetization in the recording medium causes a change in magnetic flux along the magnetic enclosure or path as described above. This results in inducing a current which flows through the coil 14, and is processed resulting in reproducing a signal corresponding to the recorded information.
In the structure of the magnetic head as explained in the first and second types of FIGS. 1, 2(a) and 2(b), a single conspicuous magnetic enclosure is formed, in other words, a single magnetic gap is formed between two magnetic poles. Though the rear or upper half portion of the coil 14 in FIG. 2(b) is covered by an upper portion 15a of the auxiliary magnetic pole, it does not form a conspicuous magnetic enclosure, therefore, it does not affect much the magnetic field in the gap G.sub.0.
Further, another type of a thin film magnetic head for perpendicular recording and reproducing is disclosed in U. S. Pat. No. 4,404,609 by R. E. Jones, Jr., issued Sept. 13, 1983. An embodiment disclosed therein provides two auxiliary magnetic poles, and the embodiment provides two magnetic gaps. The embodiment enhances magnetizing forces at a tip portion of the main magnetic pole and improves the recording and reproducing efficiency of the recording medium. A schematic cross section of the embodiment is shown in FIG. 3(a). The same reference numerals are used to denote the similar parts as those used in FIGS. 2(a) and 2(b).
The magnetic head of FIG. 3(a) has a second auxiliary magnetic pole 25 and the rear end portion thereof contacts a rear end portion 153 of the first auxiliary magnetic pole 15. The widths of the magnetic layers, which form the main magnetic pole 12 and first and second magnetic poles 15 and 25, are progressively narrower as their distance from a non-magnetic substrate 11 or slider increases. The gaps between the surface of the recording medium 2 and each pole tip are the same. The thickness of the tip portion of the main magnetic pole 12 is made less than those of other two auxiliary poles such as about 1 micron versus 2.5-3 microns.
The configuration of FIG. 3(a) has two distinct magnetic enclosures; the first enclosure starting from contact point 151, passes through main magnetic pole 12, recording medium 2, front half portion of auxiliary magnetic pole 15b, and then returns to the contact point 151 in a clockwise direction; and the second enclosure starting from contact point 151, passes through main magnetic pole 12, recording medium 2, second auxiliary magnetic pole 25, rear half of first auxiliary magnetic pole 15a, and then returns to the contact point 151 in a counterclockwise direction. Because current directions interlinking the front and rear portions 14a and 14b of the coil 14 are opposite, the magnetic fields generated in the common gap between the tip of the main magnetic pole 12 and the recording medium 2 are additive. On the other hand, the directions of magnetic force induced at the tip portion of the first and second auxiliary poles are in opposite directions with regard to that of the main magnetic pole.
The embodiment of FIG. 3(a) has the advantage that the magnetizing force in the recording medium at the tip portion of the main magnetic pole 12 is substantially enhanced by the existence of the second auxiliary magnetic pole.
When the magnetic head of this type is used, the signal generated during reproducing operation can be reshaped such as a signal shape S shown in FIG. 3(b). The signal S has a single positive pulse, and has leading and trailing negative pulses. The signal S can be sensed as a single narrow pulse by the prior art technology similar to the output of the single gap two-pole thin film transducer for longitudinal recording.
When the structure of the magnetic head disclosed in one of the above three references of the prior art is utilized, it has been found that edge noise is generated during reproducing by the auxiliary pole and can not be neglected, and this deteriorates the recording and reproducing efficiency.